To do so, first find the location of Oracle libraries. The path should be something like /usr/lib/oracle/<version>/client(64)/lib/. In my case (Ubuntu 14.04 LTS, Intel on 64-bit), it was /usr/lib/oracle/12.1/client64/lib/.

Now, add this path to the system library list. Create and edit a new file:

$ sudo nano /etc/ld.so.conf.d/oracle.conf

Add inside the path:

/usr/lib/oracle/12.1/client64/lib/

Run now the dynamic linker run-time bindings utility:

$ sudo ldconfig

For other errors when trying to run sqlplus, please consult the Ubuntu help page.

Wait! History? Auto-completion?

The weird thing about SQL*Plus is that it doesn't provide history and auto-completion like the MySQL client does. Here comes rlwrap, the "readline wrapper" — a small utility that uses the GNU readline library to allow the editing of keyboard input for any command.